The present invention relates to a telecommunication cable equipped with at least one optical fiber. In particular, the present invention relates to a telecommunication cable equipped with at least one tight-buffered optical fiber, especially suitable for indoor installations.
An optical fibre generally comprises a core surrounded by a cladding, said core and cladding being preferably made of glass, and at least one coating. The combination of core and cladding is usually identified as “optical waveguide”. Usually, the coatings of the optical waveguide are two. The coating directly contacting the optical waveguide is called “first coating” or “primary coating”, and the coating overlying the first one is called “second coating” or “secondary coating”. Typically, said first and second coatings are made of a polymeric material, such as a UV-curable acrylate polymer.
Certain applications require the optical fibre to be further coated by a buffer coating provided over the at least one coating.
Examples of these applications are indoor and premises installations, cable terminations, pigtails, patchcords and, more generally, those applications in which the optical fibre is subjected to repeated mechanical stresses because of recurring installation operations. When said buffer coating is provided substantially in contact with the at least one exterior coating it is said to be a “tight buffer”. When said buffer coating is in the form of a tube having an internal diameter larger than the overall external coating diameter (the outer diameter of the optical fiber typically is of 240-250 μm), it is said to be a “loose buffer”. Depending on the difference between the fiber outer coating diameter and the buffer inner diameter, a loose buffer can be identified as “loose” or “near tight”. Typically, a buffered optical fibre can be used as semi-finished component to form a cable in association with other components as required by the specific use to which the cable is intended. In some applications, when additional protection is not required, the buffered optical fibre can be used as such to operate as a cable.
U.S. Pat. No. 5,917,978 discloses a buffered optical fiber which includes a coated optical fiber loosely contained within a space delimited by the inner surface of a plastic tube. The outer surface of the coated optical fiber is formed of a non-stick material such as Teflon™. Due to the non-stick coating on the coated optical fiber and the air gap around it, the improved cables may be stripped to any practical length. The outer diameter of the outer coating may be approximately 273 μm. The outer diameter of tube may be about 900 μm, and the inner diameter of the tube may be in the range 300 to 500 μm, with a preferred value being 400 μm. The plastic tube may be formed of any material, such as polyvinyl chloride material, suitable for use as the jacket of a 900 μm buffered fiber. Suitable materials may have a tensile strength in the range of 2000-4000 PSI (13.8-27.6 MPa) per ASTM D-412. A vertical extrusion process may be used to form the tube about a coated optical fiber. No vacuum is applied to the extrudate forming the tube as the extrudate exits the extrusion die.
U.S. Pat. No. 6,714,713 relates to a buffered optical fiber having a core, a cladding and at least one coating, and a buffer layer generally surrounding the optical fiber, wherein the buffer layer has a portion thereof generally contacting a portion of the at least one coating, the buffer layer having an average shrinkage of about 3 mm or less from a first end of the buffered optical fiber. Moreover, a buffered optical fiber is disclosed, wherein the buffer layer has an average strip force of about 5 Newtons or less when a 50 cm length of the buffer layer is stripped from an end of the buffered optical fiber. The buffer layer can be relatively loosely or tightly disposed around the optical fiber. For example, the optical fiber can have a nominal outer diameter of about 245 microns and the buffer layer can have a nominal inner diameter (ID) of about 255 to about 350 microns, more preferably about 255 to about 320 microns, and most preferably about 255 microns to about 270 microns, with an outer diameter of up to about 900 microns. In certain applications, it may be advantageous to strip the buffer layer in long lengths, for example, 50 cm or more in one pass. Long strip lengths may be accomplished with or without interfacial layer. The material of the buffer layer can have a predetermined ultimate elongation, for example, as measured using ASTM D-412. An ultimate elongation in the range of about 300% or more, and more preferably in the range of about 325% or more and most preferably about 350% or more is desired. Moreover, the material of the buffer layer may have a Shore D hardness, measured using ASTM D-2240, in the range of about 50 to 60. Examples of materials to be used for the buffer layer are GFO 9940DW, a thermoplastic elastomer (TPE), and Elastollan® 1154 D 10 FHF (BASF), a thermoplastic polyether-polyurethane (TPU). GFO 9940DW has an ultimate elongation of about 650% (ASTM D-412), and a Shore D hardness of about 48 (ASTM D-2240). Elastollan® 1154 D 10 FHF has an ultimate elongation of about 350% (ASTM D-412), and a Shore D hardness of about 58 (ASTM D-2240).
U.S. Pat. No. 6,215,931 relates to a telecommunications cable element having a transmission element disposed in a buffer tube made from thermoplastic polyolefin elastomeric buffer material having a modulus of elasticity below about 500 MPa at room temperature and a modulus of elasticity below about 1500 MPa at −40° C. The transmission element may be an optical fiber, a bundle of optical fibers or an optical fiber ribbon. The transmission element may be disposed in the buffering tube in a tight, near-tight or loose configuration. If the modulus of elasticity and elongation at break are low enough, a tight or near-tight buffer tube or member can be easily removed without special tools and without damaging the optical fiber or fibers disposed therein. Therefore, the modulus of elasticity of the buffer material is below about 500 MPa and the elongation at break is below about 500%, preferably below about 300%, both at room temperature. One example of a thermoplastic polyolefin elastomer having the above physical characteristics is a copolymer of propylene and ethylene, preferably having more than 10% by weight of ethylene. Another example is an ultra-low density polyethylene or a copolymer of ethylene and octene, the latter being preferably present in an amount greater than 10% by weight. The thermoplastic polyolefin elastomer material may also contain organic or inorganic fillers such as talc, calcium carbonate, carbon black, aluminum trihydride, magnesium hydroxide. In the examples, the thermoplastic polyolefin elastomer material has a modulus of elasticity of 120 MPa or higher and an elongation at break of 250% or higher.